The Speedco M2 Disc Brake Mounting Kits are CNC machined out of 6061 aluminum. Each kit includes one disc brake mount, three axle blocks, and two chain-tension screws/nuts. These mounts are compatible with a size 120mm disc rotor (not included) , and will not work with a 140mm disc rotor. For optimal braking performance, we always recommend a Shimano XT/XTR hydraulic braking system.